Two or more bulked continuous filament nylon yarns to be used as pile in cut pile saxony carpets are usually ply-twisted together then heat set while traveling on a moving belt in a relaxed condition through an enclosure in which saturated steam under pressure permeates the yarn. This treatment sets the yarns in the twisted configuration so that they retain a substantial degree of twist after tufting, cutting, dyeing and wear and give an appearance of compact, columnar tuft shafts. The appearance of compact, columnar tuft shafts with well-defined tuft tips is desired for cut pile saxony carpets, as opposed to cut pile velour carpets where the appearance of tuft integrity is not desired.
Yarns which are not sufficiently twisted or heat-set lose their twist so that filaments of one tuft intermingle with those of another, giving a matted appearance.
However, ply-twisting and heat setting are both slow and expensive operations. A yarn meeting the same performance standards as ply-twisted heat-set yarn without requiring twisting could be highly desirable.